1. Field of the Invention
The present invention relates to a polycarbonate resin composition and to housings made of it for electric and electronic instruments and others. More precisely, it relates to a polycarbonate resin composition having good moldability to give moldings with good appearance, good flame retardancy, high rigidity and high impact strength, and also to housings made of the resin composition for electric and electronic instruments and others.
2. Description of the Related Art
As having high mechanical strength and good electric and optical properties, polycarbonate resins are widely used in various fields of electric and electronic instruments, car parts, office appliances, building materials, etc.
The recent tendency in those application fields is toward compact and lightweight moldings, for which is required further improvement in the properties of the molding materials. For example, in fabricating housings for portable, electric and electronic instruments, portable office appliances and others, the wall thickness of the housings must be as thin as possible. However, moldings with thin walls often have poor rigidity and low impact strength, and are easily combustible. In addition, for such moldings with thin walls, the molding materials are required to have high fluidity while they are molded.
The technical problems with such compact and lightweight moldings are being solved by the development of polycarbonate resin compositions containing various additives. However, practicable molding materials capable of being molded into thin-wall moldings which have satisfactory rigidity and impact resistance and have good appearance and which have no negative influences on the environment after scrapped are not as yet known.
In particular, regarding the negative influences of scrapped resin moldings on the environment, the problem is the formation of harmful substances from halogen-containing flame retardants that are added to the moldings for the purpose of making the moldings resistant to flames. Various methods have heretofore been investigated for attaining the flame retardancy of the resin moldings, without using halogen-containing flame retardants. For example, JP-A-62-4746 has proposed a method of alloying a butadiene-free styrene and a polycarbonate resin to give halogen-free, flame-retardant polycarbonate resins. However, the resin products produced in the proposed method could not be put into practical use, since their impact strength is extremely low. On the other hand, JP-A-2-32154 has proposed a method of alloying a styrene-containing graft copolymer such as an acrylonitrile-butadiene-styrene resin or the like, with a polycarbonate resin. The fluidity of the alloyed resins is increased and the moldability thereof is improved. However, the method is still problematic in that the alloyed resins inevitably lose the high rigidity and impact strength intrinsic to original polycarbonate resins.
In order to further improve the mechanical strength of polycarbonate resins, fibrous fillers such as glass fibers, carbon fibers and the like have heretofore been added to the resins. The fibrous fillers added to the resins could greatly improve the mechanical strength, including the rigidity, the tensile strength and the impact strength of the resins. However, increasing their amount so as to satisfactorily improve the mechanical strength of the resins will often lower the moldability of the resins and will even worsen the outward appearance of the moldings of the resins. The moldings with bad appearance are problematic in that they require surface treatment such as painting.